Poultry rotaviruses See Rotavirus A Rotavirus D rotavirus F and rotavirus G

Powassan virus (POWV) A tick-borne species in the genus Flavivirus, member of the tick-borne encephalitis virus group. Isolated from a human case of fatal encephalitis in Ontario, Canada. The virus has been recovered from ticks, Ixodes marxi and I cookei, in California, Colorado and New York State, USA and Dermacentor andersoni in South Dakota, USA. Antibodies occur in squirrels and chipmunks in Ontario. Newborn mice can be infected experimentally, but not adults.

Wilson MS et al (1979) Can Med Assoc J121, 320

Poxviridae A family of large double-stranded DNA viruses. Brick-shaped or ovoid virions, 220-450 x 140-260nm, with external coat containing lipid and tubular or globular protein structures, enclosing one or two lateral bodies, and a core which contains the genome. Buoyant density (CsCl): 1.25g/ml. There are about 100 virion proteins and many virus-induced proteins, including a DNA-dependent RNA polymerase. The genome is a single molecule of covalently closed double-stranded DNA 130-375kb in length. G+C content of vertebrate species is 35-40%. Genetic recombination occurs within genera; non-genetic reactivation occurs both within and between genera of vertebrate species. There are at least 10 major antigens in the virion, one of which cross-reacts with most vertebrate species, and there is extensive serological cross-reactivity within genera. Replication occurs in the cytoplasm with type B (viral factories) and type A (cytoplasmic accumulation) inclusion bodies. Virus is released from microvilli or by cellular disruption. Ether-sensitivity varies between genera. A hemagglutinin separate from the virion is produced by species in the genus Orthopoxvirus. There are two subfamilies: Chordopoxvirinae (poxviruses of vertebrates) and Entomopoxvirinae (poxviruses of insects) and 11 genera: Orthopoxvirus, Avipoxvirus, Capripoxvirus, Leporipoxvirus, Molluscipoxvirus, Parapoxvirus, Suipoxvirus, Yatapoxvirus and three genera of Entomopoxvirus, A, B and C.

Baxby D (1998) In Virology, vol. 1 of Topley & Wilson's Microbiology and Microbial Infections, Ninth edition, edited by BWJ Mahy and L Collier. London: Arnold, p. 367 Buller RM and Palumbo GJ (1991) Microbiol Rev 55, 80

Fenner F et al (editors) (1989) The Orthopox Viruses. New York: Academic Press poxvirus avium Synonym for Fowlpox virus.

poxvirus officinalis Name proposed for Vaccinia virus, but not adopted.

pRB A cellular tumor suppressor gene (retinoblastoma tumor suppressor) that functions in a similar way to the p53 gene in growth control and apoptosis.

Pietenpol JA et al (1996) Proc Natl Acad Sci 93, 8390

prion

PR8 A strain of human Influenza A virus, isolated in Puerto Rico in 1934.

Precarious Point virus (PPV) A tick-borne serotype in the genus Phlebovirus, member of the Uukuniemi serogroup. Isolated from Ixodes (Ceratixodes) uriae in Southern Ocean, Australia. Not associated with human disease.

precipitin An antibody which reacts with an antigen to form a precipitate (visible complex) in a precipitin reaction.

prenylation Addition of a carbon moiety derived from mevalonic acid to a cysteine located at the C-terminus of a protein. So called because prenyltransferases are responsible for the transfer of the moiety on the cysteine.

Pretoria virus (PREV) A serotype of Dera Ghazi Khan virus in the genus Nairovirus. Isolated from the tick, Argas africolumbae, in S Africa. Not reported to cause disease in humans.

primary culture The establishment of cells in culture from fresh tissue. The organized tissue needs dissociation into single cells, usually by various proteolytic enzymes (e.g. pronase or trypsin). It does not include cultures started from explants of tumors developed by injecting cultured cells into animals.

primary rhesus monkey kidney cells (PMKC) Cells used for isolation of a wide range of human viruses including influenza and other respiratory viruses.

primate adeno-associated viruses Four possible species in the genus Dependovirus referred to as types 1, 2, 3 and 4. Antigenically distinguishable by neutralization, CF and precipitin tests. There is some antigenic relationship between type 2 and 3. Type 3 species has strains K, H and T, distinguishable by neutralization. Unrelated antigenically to bovine or avian adeno-associated viruses. The presence of antibodies suggests that types 2 and 3 are human viruses and that types 1 and 4 are monkey viruses. No evidence of pathogenicity.

Berns KI (1990) Microbiol Rev 54, 316 Hoggan MD (1971) In Comparative Virology, edited by K Maramorosch and E Kurstak. New York: Academic Press, p. 43

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